Airfoils are used in many applications, typically to provide lift in a desired direction. A gurney flap, sometimes known as a wickerbill, is often used to improve the performance of the airfoil, and in its simplest form consists of a small tab projecting outwardly from the pressure side surface. Gurney flaps find particular use in applications where high amounts of lift are required, for example in a rotary wing aircraft such as a helicopter.
In order to control the amount of lift provided by the airfoils, some aircraft include deployable gurney flaps, which may be either stowed or deployed as needed. When deployed, the gurney flaps increase the lift provided by the airfoils, but increase their drag. The gurney flaps are stowed as needed to reduce drag. In some cases, the airfoil includes an opening into which the gurney flap can retract, thus withdrawing into the envelope of the airfoil. Such an opening necessarily provides ingress to particulates and atmospheric debris like dust, ice, water, insects etc., which in turn can cause wear fatigue, and degradation of the components.